Comparison of seismotectonic peculiarities of Altai Mountains and Mongolian Altai

The paleoseismogeological studies within the two representative segments of fold systems in the Altai mobile belt (Altai Mountains and Mongolian Altai) have been carried out. These studies revealed the primary seismodislocations (seismic ruptures) of both the ancient historic and prehistoric strongest earthquakes. Based on amplitudes of single displacements (reverse fault and normal fault motions were 0.5–1.6 m) and with the significant strike slip component (more than 1.5 m) taken into account, the magnitude of ancient events in the Altai Mountains was determined at approximately 7.5. The recurrence period is 1400 years on average for the M = 7.0 events and 2100 years for the M = 7.5 ones. In the western Mongolian Altai, reverse fault motions were up to 2 m, corresponding to an earthquake magnitude of about 8.0 (an analog with the 1931 Fuyun earthquake). The recurrence period for the strongest earthquakes in Mongolian Altai was longer than that for the Altai Mountains, about 3000 years. This can be explained by higher magnitude values for western Mongolian Altai. It also can be concluded that the seismic regimes of the Altai Mountains and Mongolian Altai remained almost unchanged during the entire Holocene.